A storage system is a computer that provides storage service relating to the organization of information on writable persistent storage devices, such as memories, tapes or disks. The storage system is commonly deployed within a storage area network (SAN) or a network attached storage (NAS) environment. When used within a NAS environment, the storage system may be embodied as a file server including an operating system that implements a file system to logically organize the information as a hierarchical structure of directories and files on, e.g. the disks. Each “on-disk” file may be implemented as a set of data structures, e.g., disk blocks, configured to store information, such as the actual data for the file. A directory, on the other hand, may be implemented as a specially formatted file in which information about other files and directories are stored.
The file server, or filer, may be further configured to operate according to a client/server model of information delivery to thereby allow many client systems (clients) to access shared resources, such as files, stored on the filer. Sharing of files is a hallmark of a NAS system, which is enabled because of its semantic level of access to files and file systems. Storage of information on a NAS system is typically deployed over a computer network comprising a geographically distributed collection of interconnected communication links, such as Ethernet, that allow clients to remotely access the information (files) on the filer. The clients typically communicate with the filer by exchanging discrete frames or packets of data according to pre-defined protocols, such as the Transmission Control Protocol/Internet Protocol (TCP/IP).
In the client/server model, the client may comprise an application executing on a computer that “connects” to the filer over a computer network, such as a point-to-point link, shared local area network, wide area network or virtual private network implemented over a public network, such as the Internet. NAS systems generally utilize file-based access protocols; therefore, each client may request the services of the filer by issuing file system protocol messages (in the form of packets) to the file system over the network identifying one or more files to be accessed without regard to specific locations, e.g., blocks, in which the data are stored on disk. By supporting a plurality of file system protocols, such as the conventional Common Internet File System (CIFS), the Network File System (NFS) and the Direct Access File System (DAFS) protocols, the utility of the filer may be enhanced for networking clients.
A SAN is a high-speed network that enables establishment of direct connections between a storage system and its storage devices. The SAN may thus be viewed as an extension to a storage bus and, as such, an operating system of the storage system enables access to stored information using block-based access protocols over the “extended bus”. In this context, the extended bus is typically embodied as Fibre Channel (FC) or Ethernet media adapted to operate with block access protocols, such as Small Computer Systems Interface (SCSI) protocol encapsulation over FC or TCP/IP/Ethernet.
A SAN arrangement or deployment allows decoupling of storage from the storage system, such as an application server, and some level of information storage sharing at the application server level. There are, however, environments wherein a SAN is dedicated to a single server. In some SAN deployments, the information is organized in the form of databases, while in others a file-based organization is employed. Where the information is organized as files, the client requesting the information maintains file mappings and manages file semantics, while its requests (and server responses) address the information in terms of block addressing on disk using, e.g., a logical unit number (lun).
In certain storage system network environments, clients and/or users may desire the ease of use of a name space associated with a file-based protocol, such as that used in a NAS system. However, NAS-based protocols are typically slower than those utilized in a SAN environment due to increased protocol overhead. Previous storage system implementations typically utilized an approach that “disposed” the NAS capabilities over the SAN storage system platform using, e.g., a “sidecar” device attached to the SAN platform. An example of such a prior system is the Symetrix® System platform available from EMC® Corporation. Broadly stated, individual disks of the SAN storage system, i.e., Symetrix® System, are allocated to the NAS sidecar device (e.g., a Celera™ Device) that, in turn, exports those disks to NAS clients via, e.g., the NFS and CIFS file-based protocols.
In use, client of the storage system accesses the sidecar device to obtain a set of logical block addresses associated with the file to be accessed. The client of the storage system accesses the sidecar device by sending a set of file block numbers (FBNs) to the sidecar device. A FBN is a number describing a particular block within a file, with the first block of the file being numbered as FBN number one and each block thereafter being sequentially increased. A FBN does not necessarily bear a given relation to the location of data stored on physical blocks on a storage device, such as a disk, but instead refers to the actual ordering of data within a file. From the sidecar device, the client receives a set of logical block addresses (LBAs) that reference actual physical blocks stored on the disks storing the data. For example, file block number one of a particular file may map to a logical block address of, for example, 5,016th. In other words, the first file block, containing the initial data of the file, is stored in the 5,016th disk block on the set of disks storing the file.
The client then accesses the conventional SAN storage system using the set of logical block addresses obtained from the NAS sidecar. For example, a client may issue a small computer system interface (SCSI) command to the SAN storage system. In accordance with the SCSI protocol, locations within a file must be specified using a set of logical block addresses. Thus, the client utilizes the mapped LBAs obtained from the sidecar device in requesting its desired SCSI operation. A noted disadvantage of this approach is that the client software must be modified to incorporate the additional look up and mapping functionality required to enable the client to effectuate a sidecar FBN to LBA look up operation. This requirement adds additional complexity to the client and may generate incompatibility issues with other software executing on the client. Additionally, a provider of such storage systems must develop and implement a client-side mapping software module for each type of client system to be supported. Another noted disadvantage of such sidecar systems is that the client typically is required to send look up commands to the sidecar device over a NAS network path, which is typically slower than network paths utilized in a SAN environment. This increased use of typically slower network connections substantially impairs a storage system's performance by increasing the processing overhead required.
Thus, it is an object of the present invention to provide a system and method for a client to utilize the high-speed capabilities of a SAN arrangement for data access operations to the storage system without requiring modification of the client to utilize a sidecar type device.